Back when I was shooting with a 35-mm SLR camera, I used a variety of filters but sold them all long ago. Now that I’ve bought an Olympus E-M5, I’m wondering what filters I should get. Or do I need any at all for digital photography?
Good question, BTJ, and the short answer is that one filter remains an essential accessory: the circular polarizer. While the effects provided by most other filters can be achieved with in-camera features (such as White Balance control) or with image-editing software, nothing can replicate the effects of a polarizer. It’s very useful for wiping glare from reflective surfaces to reveal the true colour of the subject and also for cutting through haze for more snappy contrast. You can darken and enrich colours with software too, but you’ll get better results by using a polarizer when taking the photos. Also check out this Q&A item: “What do I need to do to get a good exposure when using a polarizer?”
Landscape photographers often use a graduated neutral density filter (with a clear half and a grey half) that makes it easy to darken a very bright sky when taking a photo. Some photographers use UV filter on their lenses to protect the front element, citing examples where a filter saved the front element of an expensive lens from scratches. Others insist that a lens hood should provide adequate protection. If you decide to use a UV filter, be sure to remove it in strong side or backlighting to reduce the risk of flare that can degrade contrast.
Regardless of the filters you buy, insist on superior multi-layer (anti-reflective) coatings for maximum light transmission and for minimizing flare as discussed in a previous Q&A: “What are the differences between a $79 filter and a $250 filter?“